The present invention relates to heat pumps, and particularly to heat pumps that may be employed for supplying a heating cycle and a process water cycle.
WO 2007/118482 discloses a heat pump with an evaporator for evaporating water as the working liquid to produce working vapor. The heat pump further includes a compressor coupled to the evaporator to compress the working vapor. Here, the compressor is formed as a flow machine, wherein the flow machine comprises a radial wheel accepting uncompressed working vapor at its front side and expelling same by means of correspondingly formed blades at its side. By way of the suction, the working vapor is compressed so that compressed working vapor is expelled on the side of the radial wheel. This compressed working vapor is supplied to a liquefier. In the liquefier, the compressed working vapor, the temperature level of which has been raised through the compression, is brought into contact with liquefied working fluid, so that the compressed vapor again liquefies and thus gives off energy to the liquefied working fluid located in the liquefier. This liquefier working fluid is pumped through a heating system by a circulation pump. In particular, a heating flow, at which warmer water is output into a heating cycle, such as a floor heating, is arranged to this end. A heating return then again feeds cooled heating water to the liquefier so as to be heated again by newly condensed working vapor.
This known heat pump may be operated as an open cycle or as a closed cycle. The working medium is water or vapor. In particular, the pressure conditions in the evaporator are such that water having a temperature of 12° C. is evaporated. To this end, the pressure in the evaporator is at about 12 hPa (mbar). By way of the compressor, the pressure of the gas is raised to, e.g., 100 mbar. This corresponds to an evaporation temperature of 45° C. thus prevailing in the liquefier, and particularly in the topmost layer of the liquefied working fluid. This temperature is sufficient for supplying a floor heating.
If higher heating temperatures are required, more compression is adjusted. However, if lower heating temperatures are needed, less compression is adjusted.
Furthermore, the heat pump is based on multi-stage compression. A first flow machine is formed to raise the working vapor to medium pressure. This working vapor at a medium pressure may be guided through a heat exchanger for process water heating so as to then be raised to the pressure needed for the liquefier, such as 100 mbar, e.g. by a last flow machine of a cascade of at least two flow machines. The heat exchanger for process water heating is formed to cool the gas heated (and compressed) by a previous flow machine. Here, the overheating enthalpy is utilized wisely to increase the efficiency of the overall compression process. The cooled gas is then compressed further with one or more downstream compressors or directly supplied to the liquefier. Heat is taken from the compressed water vapor so as to heat process water to higher temperatures than, e.g., 40° C. therewith. However, this does not reduce the overall efficiency of the heat pump, but even increases it, because two successively connected flow machines with gas cooling connected therebetween achieve the demanded gas pressure in the liquefier with a longer life due to the reduced thermal stress and with less energy than if a single flow machine without gas cooling were present.
In heating systems, a process water tank of its own may be arranged, which holds a certain amount of process water which is heated to a certain default warm-water temperature. This process water tank typically is dimensioned so that warm water can be dispensed at default temperature for a certain period of time, e.g. for filling a bathtub. For this reason, a mere flow-type heating principle often is not employed in process water heating when no combustion processes are to be employed for process water heating, but a certain process water volume is kept at the specified temperature instead.
This process water tank should, on the one hand, not be too large, so that its thermal inertia does not become too great. On the other hand, this process water tank should not be too small either, so that a minimum amount of warm water can be tapped quickly, without the temperature of the warm water decreasing significantly, which would detract from the convenience of the heating.
At the same time, the process water tank should be sufficiently insulated, since heat loss via the process water tank is especially disadvantageous. Thus, this heat loss has to be compensated for, to ensure that a sufficiently large amount of warm process water is available at all times. This means that the heating must also operate when there currently is no demand, but when the contents of the process water tank have been cooled due to bad insulation.
This means that the process water tank is to be insulated especially well, which again entails both space for insulating materials and costs of the insulating materials.
Moreover, a heating system, so as to be well accepted on the market, must not be too bulky and should be offered in a form ensuring ease of handling by workmen and builder-owners, and can easily be transported and set up at typical locations, such as in cellars or heating rooms. Special insulation for the process water tank could indeed be built in on location so as to keep the volume of the overall heating system small for transportation and setup on location. On the other hand, each step of later assembly of a heating system leads to costs for the workman and at the same time also to additional fault liability. Moreover, the insulation material needed for insulating the process water tank also is expensive if good insulation effects are to be achieved. However, an insulation effect is important especially for heat pumps to be used in smaller buildings, since such heat pumps are to be used in large numbers and should be optimized for high efficiency, i.e. the ratio of expended energy to extracted energy, so that maximum energy efficiency is achieved on the whole.